The invention relates to a flowmeter having a cast metal housing, a rectangular airflow channel therewithin, and a transversely-extending, trapezoidal pivotal baffle plate particularly for measurement of the air drawn in by an internal combustion engine through the air intake duct.
Flowmeters of this kind are already known, for example, they are used in fuel injection systems to ascertain the volume of air drawn into internal combustion engines. In a typical application, the transversely-extending pivotal baffle plate is deflected by a throttle-induced increase in the air flow until substantially the entire rectangular cross section of the flow channel is unrestricted. In addition, a spring mounted on the pivot shaft serves as an opposing force to the air pressure exerted on the baffle plate, so that the angular deflection of the baffle plate is a measure of the volume of air flow through the channel. The housings of these known flowmeters are, e.g., zinc castings. A circumferential clearance is provided between the baffle plate edges and the flow channel wall, amounting to approximately 0.1 to 0.2 mm total. Though a narrow circumferential edge clearance is, for functional reasons, normally provided, a concomitant problem may result due to unrelieved internal stresses in the cast metal housings so that in applications over a broad operating temperature range of the engine, e.g., from -40.degree. C. to +120.degree. C., the castings may expand unevenly and the damping flap or baffle plate may make contact with the walls of the flow channel or damping chamber, thus impeding their free pivotal motion.